System and method for precision transport, positioning, and assembling of longitudinal nano-structures

ABSTRACT

A method for assembling multi-component nano-structures that includes dispersing a plurality of nano-structures in a fluid medium, and applying an electric field having an alternating current (AC) component and a direct current (DC) component to the fluid medium containing the plurality of nano-structures. The electric field causes a first nano-structure from the plurality of nano-structures to move to a predetermined position and orientation relative to a second nano-structure of the plurality of nano-structures such that the first and second nano-structures assemble into a multi-component nano-structure.

CROSS-REFERENCE OF RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.61/157,032 filed Mar. 3, 2009, the entire contents of which are herebyincorporated by reference.

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Grant No.DMR04-03849 awarded by the National Science Foundation.

BACKGROUND

1. Field of Invention

The current invention relates to methods and systems for assemblingmulti-component nano-structures and novel multi-componentnano-structures.

2. Discussion of Related Art

The study of nano-materials often includes fabrication,characterization, and applications of the nano-structures. A vastvariety of nano-structures made of metallic, semiconductive, magnetic,and polymer materials have been fabricated into OD dots (S. Link and M.A. El-Sayed, J. Phys. Chem. B, 103, 8410 (1999)), rings, 1D wires/tubes(F. Q. Zhu, G. W. Chem, 0. Tchernyshyov, X. C. Zhu, J. G. Zhu and C. L.Chien, Phys. Rev. Lett. 96, 27205 (2006)), 2D films (K. Robbie and M. J.Brett, J. Vac. Sci. Tech. A. 15, 1460 (1997)), and 3D architectures (J.E. G. J. Wijnhoven and W. L. Vos, Science, 281, 802, (1998)).

Among them, 1D nano-structured wires/tubes have become the focus ofrecent research. Extensive work reveals that nano-wires and nano-tubeshave unique electronic (Z. Zhang, X. Sun, M.S. Dresselhaus and J.Y.Ying, Phys. Rev. B. 61, 4850 (2000)), optical (X. Lu, T. Hanrath, K. P.Johnston and B. A. Korgel, Nano Lett. 3, 93 (2003). T. T. Hanrath andB.A . Korgel, J. Am. Chem. Soc. 124, 1424 (2001). J. D. Holme, K. P.Johnston, R. C. Doty and B. A. Korgel, Science, 287, 1471 (2000)),magnetic (T. M. Whitney, J. S. Jiang, P. C. Searson, and C. L. Chien,Science 261, 1316 (1993)), and mechanical properties (E. W. Wong, P. E.Sheehan and C. M. Lieber, Science, 277, 1971 (1997)), owing to thequantum confinement effect and large surface area.

Even though device prototypes made of nano-wires and nano-tubes havebeen demonstrated, such as logic units (Y. Huang, X. Duan, Y. Cui, L.J.Lauhon, K.-H. Kim and C. M. Lieber, Science, 294, 1313 (2001)) inmicrochips, nano-lasers (M. Huang, S. Mao, H. Feick,d H. Yan, Y. Wu, H.Kind, E. Weber, R. Russo and P. Yang, Science, 292, 1897, (2001)),optical switches (H. Kind and H. Yan and M. Law and B. Messer and P.Yang, Adv. Mater. 14, 158 (2002)), and sensors for cellular andmolecular diagnosis (S. R. Nicewarner-Pena, R. G. Freema, B. D. Reiss,L. He, D. J. Pena, D. Walton, R. Cromer, C. D. Keating and M. J. Natan,Science, 294, 137, (2001). Y. Cui and Q. Wei and H. Park and C. M.Lieber, Science, 293, 1289, (2001)), the application of nano-wires astechnologically useful materials has been greatly hindered by thedifficulties in precision handling of nano-wires.

To date, nano-wires containing magnetic segments have been aligned byapplying external magnetic fields using electromagnets or permanentmagnets over centimeter lengths (M. Chen, L. Sun, J. E. Bonevich, D. H.Reich, C. L. Chien, and P. C. Searson, Appl. Phys. Lett., 82, 3310(2003). M. Tanase, L. A. Bauer, A. Hultgren, D. M. Silevitch, L. Sun, D.H. Reich, P. C. Searson, and G. J. Meyer, Nano Lett., 1, 155 (2001)). Amagnetic segment is incorporated into the nano-wires to achieve thealignment. Because the magnetic force is a weak force, it is difficultto induce any motion on nano-wires. More recently, holographic opticaltraps have been used to manipulate semiconductive nano-wires (R.Agarwal, K. Ladavac, Y. Roichman, G. Yu, C. M. Lieber, D. Grier, Opticalexpress, 13, 8906 (2005)). The efficiency, however, is quite low becauseonly several nano-wires can be manipulated at a time. Elaborateinstrumentations are also required. Dielectrophoretic force induced byAC electric fields has been used to transport nano-wires and nano-tubes(D. L. Fan, F. Q. Zhu, R. C. Cammarata and C. L. Chien, Appl. Phys.Lett. 85, 4175 (2004); B. Edwardsa, N. Engheta, S. Evoy, I Appl. Phy.102, 024913 (2007)). However, the direction, velocity, or t rajectorycannot be controlled without extremely complicated electronic design andcomputer programming. Thus, there is a need in the art for improvedmethods and systems for precision manipulation of nano-structures.

SUMMARY

Some embodiments of the current invention provide a method forassembling multi-component nano-structures that includes dispersing aplurality of nano-structures in a fluid medium, and applying an electricfield having an alternating current (AC) component and a direct current(DC) component to the fluid medium containing the plurality ofnano-structures. The electric field causes a first nano-structure fromthe plurality of nano-structures to move to a predetermined position andorientation relative to a second nano-structure of the plurality ofnano-structures such that the first and second nano-structures assembleinto a multi-component nano-structure.

Some embodiments of the current invention provide a system forassembling multi-component nano-structures that includes a sample holderdefining a sample chamber therein, the sample chamber being suitable tohold a fluid having a plurality of nano-structures suspended in thefluid; first and second electrodes spaced apart with the s ample chamberarranged between them; a voltage source electrically connected to thefirst and second electrodes; and a voltage controller in communicationwith the voltage source. The voltage source is suitable to provide acombined DC voltage and AC voltage in response to the voltage controllerto cause a nano-structure of the plurality of nano-structures to becomeoriented in a predetermined orientation and to move to a predeterminedposition.

Some embodiments of the current invention include novel multi-componentnano-structures. A multi-component nano-structure comprises a firstnano-structure having a first magnetic segment; and a secondnano-structure having a second magnetic segment. The first and secondnano-structures form a multi-component nano-structure via an interactionof the first and second magnetic segments.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objectives and advantages will become apparent from aconsideration of the description, drawings, and examples.

FIG. 1A is a schematic illustration of a system for transporting,positioning, and assembling nano-structures according to someembodiments of the current invention.

FIG. 1B is a schematic illustration of a computer controlled system fortransporting, positioning and assembling nano-structures according to anembodiment of the current invention.

FIG. 2 is a schematic illustration of a microchip for precisionmanipulation of nano-structures according to an embodiment of thecurrent invention.

FIG. 3 is a schematic illustration of various voltage configurations onquadruple electrodes and the respective effects on movingnano-structures according to an embodiment of the current invention.

FIG. 4A shows the characterization of the alignment rate of nano-wiresin an alternating current (AC) electric field according to someembodiments of the current invention.

FIG. 4B shows the measured velocity of nano-wires as a function ofapplied direct current (DC) voltages according to some embodiments ofthe current invention.

FIG. 5 shows the measured velocity of multi-wall carbon nano-tubes as afunction of applied DC voltages according to some embodiments of thecurrent invention.

FIG. 6 shows example trajectories of nano-structures being manipulatedaccording to some embodiments of the current invention.

FIG. 7A shows a nano-pillar according to an embodiment of the currentinvention.

FIG. 7B shows an array of nano-wires mounted on nano-pillars accordingto an embodiment of the current invention.

FIG. 7C shows a close-up view of two nano-wires mounted on two nano-pillars according to an embodiment of the current invention.

FIG. 8A shows a nano-motor assembled according to an embodiment of thecurrent invention.

FIG. 8B shows the measured rotation angle and angular rotation speed ofa nano-motor assembled according to an embodiment of the currentinvention.

FIG. 8C shows the two measured angular rotation speeds of a nano-motorassembled according to an embodiment of the current invention.

FIG. 8D shows an array of nano-motors assembled according to anembodiment of the current invention.

FIG. 8E shows a 2x2 array of the nano-motors in an induced rotary motionaccording to some embodiments of the current invention.

FIG. 9A shows a nano-oscillator assembled according to an embodiment ofthe current invention.

FIG. 9B shows the assembled nano-oscillator of FIG. 9A at various phasesin an oscillatory motion.

FIG. 9C shows the measured oscillation angle of the nano-wire oscillatoras a function of time.

DETAILED DESCRIPTION

Some embodiments of the current invention are discussed in detail below.In describing embodiments, specific terminology is employed for the sakeof clarity. However, the invention is not intended to be limited to thespecific terminology so selected. A person skilled in the relevant artwill recognize that other equivalent components can be employed andother methods developed without departing from the broad concepts of thecurrent invention. All references cited herein are incorporated byreference as if each had been individually incorporated.

FIG. 1A shows a system for transporting, positioning, and assemblingnano- structures according to some embodiments of the invention. Theterm nano-structure is intended to structures that have at least onedimension that is smaller than 1 μm. This includes structures in whichall dimensions are less than 100 nm, but it is not limited to only suchstructures. In some embodiments, the nano-structures may have alongitudinal dimension of less than 100 μm and a lateral dimension ofbetween 2 nm and 400 nm. In some embodiments, the nano-structures mayhave a longitudinal dimension of less than 30 μm and a lateral dimensionof between 5 nm and 400 nm. In some embodiments, the nano-structures mayhave a longitudinal dimension of less than 1 μm and a lateral dimensionof between 5 nm and 100 nm. Generally, as long as the nano-structure hasan asymmetry such that one dimension is longer than the other two and itis sufficiently small to disperse in fluid, such as de-ionized water,for a long enough time to be assembled, this system can be useful. Thenano-structures can be, for example, nano-wires, nano-fibers,nano-tubes, nano-spheres, nano-disks, nano-plates, nano-cubes,nano-cylinders, and variants thereof. The nanostructures can also beattached to macrostructures in some embodiments and/or tonano-structures that are integral or attached to a macrostructure. Forexample, nano-pillars, nano-spheres, nano-cubes that are attached to orintegral with a substrate can be included in assembly processesaccording to some embodiments of the current invention.

A voltage source 101 provides a voltage to electrodes 102. The voltagesource can apply both a direct current (DC) and alternating current (AC)voltage. The electrodes can be less than 1 mm in length, for example, insome embodiments. The electrodes can be microelectrodes in someembodiments, but they are not limited to microelectrodes in allapplications. The pair of electrodes 102 are spaced around a samplechamber 103 that is suitable to hold a fluid medium containingnano-structures in suspension. The voltage applied on the electrodes 102induces an electric field that encompasses the nano-structures insuspension. The electric field causes positional and orientationalchanges of the nano-structures. One, two, or three pairs of electrodesmay be spaced around sample chamber 103 to provide a suitable electricfield in the sample chamber 103 to manipulate suspended nano-structuresin a two-dimensional plane or a three-dimensional volume. The electrodesmay be constructed on a substrate by, for example, lithography.De-ionized water has been found to be a suitable fluid medium for use influid chamber 103 according to some embodiments of the currentinvention. Sample chamber 103 can be less than 1 mm in length in someembodiments. The electrodes 102 and the sample chamber 103 can alsotogether form a sample holder according to some embodiments of thecurrent invention.

An observation device 104 is arranged to monitor positions of thenano-structures in the sample chamber 103. To track the positions ofnano-structures, the observation device 104 may comprise at least one ofa microscope, an imaging device, such as a charge-coupled device (CCD)camera, an infra-red camera, or a radiation detector. Thenano-structures can be tagged with, for example, relevant fluorescent,infra-red or radioactive markers in some embodiments, but is notrequired in all cases. Observation device 104 may be further adapted torecognize changed positions and orientations of the nano-structures andto provide data encoding the changed positions and/or orientations. Whenthree pairs of electrodes provide an electric field to manipulate thenano-structures in three dimensions, at least one electrode can betransparent in an operating wavelength of observation device 104.

A controller 105 is in communication with observation device 104 toreceive information representing the positions and orientations of thenano-structures. Controller 105 is also in communication with voltagesource 101. Controller 105 is configured to control a parameter of thevoltage that can cause the nano-structures to change positions ororientations in the fluid medium of sample chamber 103. The parametercan be amplitude, frequency, phase, or duty cycle of the appliedvoltages, or variations thereof. Controller 105 can also be furtherconfigured to adjust the parameter of the voltage based on data fromobservation device 104 to take into account the changed positions and/ororientations of the nano-structures in real time according to someembodiments of the current invention. The controller 105 can be acomputer having a processor, a memory, a display device, and an inputdevice according to some embodiments of the current invention. Thedisplay device can be, for example, a cathode ray tube (CRT) monitor, aliquid crystal display (LCD) monitor, a digital light projection (DLP)monitor, a projector display, a laser projector, a plasma screen, anorganic light emitting diode (OLED), etc. The input device can be, forexample, a keyboard, a mouse, a touch screen, a joy-stick, etc. However,the display and input devices are not limited to these particularexamples. They can include other existing or future developed displayand input devices without departing from the scope of the currentinvention.

FIG. 1B shows a computer controlled system for transporting,positioning, and assembling longitudinal nano-structures according to anembodiment of the current invention. Computer-controllable electriccircuitry can selectively power the electrodes 102 in this embodiment.The circuitry is one embodiment of voltage source 101. An opticalmicroscope coupled to a video camera (e.g., a CCD camera) may be used tocapture the motion of the nano-structures in the horizontal plane forsubsequent analysis of their motion. The optical microscope coupled to avideo camera is one embodiment of observation device 104. When threepairs of electrodes provide an electric field to manipulate thenano-structures in three dimensions, one of the microelectrodes may besubstantially transparent within an operating wavelength of themicroscope and the video camera to facilitate inspection ofnano-structures in sample chamber 103. In some embodiments, a computerprogram on the computer may recognize the positions, orientations,trajectories, and velocities of longitudinal nano-structures beingmonitored. The computer running the computer program may direct thecircuitry to selectively apply the voltages on the electrodes 102 totransport nano-structures to designated positions and orientations. Thecomputer is only one example of an embodiment of controller 105.

FIG. 2 is a schematic illustration of a microchip for precisionmanipulation of nano-structures according to some embodiments of thecurrent invention. In this example, the microchip includes electrodesand a sample chamber combined into the combined structure. The microchipincludes a glass substrate in this example. The broad concepts of theinvention are not limited to a particular material of the substrate.Some suitable materials may include, for example, quartz, glass,silicon, selenium, GaAs, ZnO, polymer, etc. Two pairs of parallelmicroelectrodes (each electrode has a dimension of 480 μm x 480 μm) maybe constructed on an insulating substrate via lithographic methods. Onceenergized with a voltage, an electric field is generated between themicroelectrodes. A polydimethylsiloxane (PDMS) elastomer well 5 mm indiameter and 5 mm in thickness may be firmly attached on top of themicroelectrodes. The well may hold a non-ionized fluid medium in whichnano-structures are suspended. The well can be covered by a piece ofglass slide, for example, to prevent water evaporation. The transparentglass cover may enable the motion of the nano-structures to bevisualized by, for example, an optical microscope coupled to a videocamera.

Nano-structures suspended in a liquid such as water typically absorbions from the liquid and, as a result, usually carry charges. Theabsorbed ions can be positive or negative, depending on the fluid, thematerial of the nano-structure, the pH value, the type and concentrationof salt in the fluid.

The surface of the nano-structures can also be charged by chemicalmodifications. For example, the surface of the nano-structures can bemodified by molecules with one end attached to the nano-structures andthe other end carry charges when ionized in a liquid. For demonstrationpurpose, Au nano-wires have been surface modified by thiol-conjugation.Molecules with thiol group (-SH) at one end and carboxyl group (-COOH)or amino group (−NH₂) at the other end are conjugated on the surface ofAu nano-wires. After suspension in de-ionized (DI) water, the carboxylgroup (-COOH) may be ionized to become COO″, and the amino group (−NH₂)may be ionized to become −NH³⁺. Thus, the nano-wires surface terminatedby the carboxyl group (-COOH) are negatively charged in DI water. Thoseterminated by the amino group (−NH₂) are positively charged in DI water.

When a charged nano-structure is exposed to an electric field, thenano-structure experiences a force resulting from a coulomb interactionbetween the electric field and the charge. This force is calledelectrophoretic force (EP) for particles suspended in a liquid. The EPforce is characterized as:

{right arrow over (F)}_(EP)=q{right arrow over (E)} (1)

The particle is driven by the EP force to move at a constant terminalvelocity {right arrow over (v)} determined by the viscous force of theliquid:

q{right arrow over (E)}=Kη{right arrow over (v)} (2),

where q is the total charges on the surface of the particle, {rightarrow over (E)} is the electric field strength, K is the stokes shapefactor of the particle, and η is the viscosity of the liquid. The EPforce can therefore drive charged nano-structures suspended in liquidsinto motion.

The dielectrophoretic (DEP) force is the force a charge-neutralnano-structure experiences in an AC electric field due to an interactionbetween the AC field and the polarization of the nano-structure causingan induced electrical dipole moment. Theoretically, DEP force works forboth DC and AC electric fields. Practically, however, most DEP phenomenaare studied at high frequency electric fields (>100 Hz) to circumventthe screening effect by water which has a large dielectric constant of80, thus reducing the DEP force by a factor of 6400. The DEP force canalign, for example, nano-wires in the direction of the electric field,and transport the nano-wires to the spatial location of the largestelectric field gradient.

If a uniform AC electric field with no applied gradient, the DEP forcewould only align but would not transport the nano-structures. Thisfeature provides us with the possibility of using a uniform AC electricfield to align the nano-structures and a uniform DC electric field totransport the charged nano- structures independently.

FIG. 3 shows schematics of various voltage combinations provided to aquadruple electrode and the respective effects on transportingnano-structures in suspension. Different combinations of alternatingcurrent (AC) and direct current (DC) electric field components mayaffect the motions of nano-structures differently. For example, when theAC and DC electric field components are parallel in direction (FIG. 3A),the nano-structures may be moving with their longitudinal dimensionparallel to the direction of the AC and DC electric field, as shown inFIGS. 3D and 3G for Au nano-wires and carbon nano-tubes, respectively.When the AC and DC electric field components are perpendicular indirection (FIG. 3B), the nano-structures move with their longitudinaldimension perpendicular to the DC electric field direction and parallelto the AC electric field direction, as shown in FIGS. 3E and 3H for Aunano-wires and carbon nano-tubes, respectively. When only the DCelectric field is present (FIG. 3C), the nano-structures move along atrajectory with their longitudinal dimension in random orientations, asshown in FIGS. 3F and 31 for Au nano-wires and carbon nano-tubes,respectively. FIG. 3 shows that the AC electric field can accuratelycontrol the orientation of the nano-structures, independent of themotion. FIG. 3 also shows that both nano-wires (150 nm in radius) andmulti-wall nano-tubes (10˜25 nm in radius) can be manipulated insuspension.

Nano-structures in suspension may be placed in the center region of thequadruple electrodes. The nano-structures can be maintained there forapproximately 20 seconds to settle, before voltages are applied to theelectrodes. The AC voltages can be from 2 V to 8 V, with a frequencyfrom 10 MHz to 50 MHz in some applications of the current invention. DCvoltages can be between 1 V to 2.5 V, for example. The DC voltages canbe chosen to be below 3 V to avoid electrohydrolysis of water.

Further, the nano-structures can be manipulated in three dimensions. Inaddition to the quadruple electrodes on the substrate, another pair ofelectrodes can be added perpendicular to the substrate to provide theelectric field in the third dimension. Thus, the nano-wires can bemanipulated with all the versatilities described above and in threedimensions.

FIG. 4A shows the characterization of the alignment rate of nano-wiresin an alternate current (AC) electric field according to someembodiments of the current invention. The angles between thelongitudinal dimension of the nano-wires and the trajectories of theirmotion in the electric field were measured. The time dependence of thestandard deviation of angle (σ_(angle)) among all nano-wires in thevideo are displayed in FIG. 4A. The uniform AC electric field was turnedon at t =0. The value of σ_(angle), decreases rapidly from about 60° (inthe random arrangement) to about 5° , approximately 1 second after theuniform electric field has been turned on and remains so. For thetranslational motion, the nano-wires moved in a linear trajectory in thedirection of the DC electric field as shown in the inset of FIG. 4A.When the direction of the DC electric field was reversed, the nano-wiresreversed their motion and retraced the previous trajectories as shown inFIG. 4A.

FIG. 4B shows the measured velocity of nano-wires as a function ofapplied direct current (DC) voltages. The velocity of nano-wires shouldincrease linearly with the strength of the DC electric field accordingto the relation of v=qE/Kη, where the electric field E is proportionalto the applied voltage V for a fixed electrode configuration.Experimentally, the terminal velocity of the Au nano-wires has beenconfirmed to be proportional to V. This result is shown in FIG. 4B forboth longitudinal and transverse motion of negatively charged Aunano-wires. The terminal speed reached can be as much as 40 μm/s; a veryhigh speed in the microscopic world. The difference in the speeds forlongitudinal and the transverse motion, shown in FIG. 4B, indicates thatthe viscous force may depend on the orientations of the nano-structures.

FIG. 5 shows the measured velocity of multi-wall carbon nano-tubes(MWCNTs) as a function of applied DC voltages. The velocities weremeasured from MWCNTs (10˜25 nm in radius) suspended in DI water (shownin FIGS. 3G-3I). The plot using squares is from measured positional dataof transporting MWCNTs with parallel AC and DC field components. Theplot using dots is from measured positional data of transporting MWCNTswith perpendicular AC and DC field components. The plot using circles isfrom measuring positional data of transporting MWCNTs with only DC fieldcomponents. The moving velocities are linearly proportional to theapplied DC voltages, similar to the proportionality seen in FIG. 4B fornano-wires. Because of the smaller size of MWCNT, the orientationdependence of the viscous force may be less pronounced.

Having demonstrated that charged nano-wires can be moved along astraight line with specific speed and orientation, both forward andbackward, FIG. 6 shows this manipulation can be extended to twodimensions by using two pairs of parallel electrodes, such as shown inFIG. 3, to control the motion and the orientation along the twoorthogonal directions. A single nano-wire can be moved from any initiallocation at the coordinate of (X_(i), Y_(i)) to any final location atthe coordinate of (X_(f), Y_(f)) by supplying a series of voltages withcertain durations so that the nano-wire can be moved with a net distanceof X_(f)- X₁ and Y_(f)-Y_(i) in the two directions. The sequence ofthese voltage pulses can be mixed to provide many different pathsconnecting the two locations. The path can even include curvedtrajectories when small voltage step sizes are being used.

In FIG. 6A, several nano-wires were moved from their initial locationsto the final locations and back to the initial locations followingzigzag paths comprising straight segments along the X and Y axes. InFIG. 6B, the nano-wires were moved in the trajectory of squares, bothclockwise and counterclockwise, by a programmed application of voltagesprovided to the microelectrodes. The nano-wires were transported withtheir longitudinal dimension aligned with the direction of thetransport. As soon as the spatial orientation of the AC electric fieldwas turned 90° , the orientation of the nano-wires followed within about1 second in response. When all the nano-wires had been driven back tothe original locations, after traveling hundreds of micrometers, theywere within only a few micrometers from their starting locations asshown in the insets of FIGS. 6A and 6B. This demonstrates the precisionof the manipulation is largely limited by the Brownian motion of thenano-wires in suspension. These examples demonstrate that this methodcan transport and position nano-wires to any location along anyprescribed trajectory with sub-micrometer precision.

By using this two-dimensional manipulation technique, two oppositelycharged 6-μm-long Au nano-wires in suspension were successfullyconnected. Two oppositely charged nano-wires were aligned and moved inopposite directions, either away or towards each other depending on thedirection of DC electric field. By manually controlling the sequence ofvoltages supplied to the electrodes, two Au nano-wires carrying oppositecharges, initially separated by 185 μm, were moved towards each other,as shown by the overlap images in FIG. 6C, where the two nano-wires wereeventually connected tip to tip. The charges on the two nano-wires wereunequal with a ratio of about 2 to 1, as can be inferred from thedistances traversed by the nano-wires in FIG. 6C. Because the twonano-wires had a radius of only 150 nm, the high precision of themanipulation had been demonstrated.

When the two nano-wires are loosely joined, the Brownian motion willdisconnect the two joined Au nano-wires once the electric field isremoved. However, the joint can be secured by, for example, a chemicalbonding through suitable processing of the surface of the Au nano-wire.Another example of securing the joint is by adding short Ni segments(0.5 μm) at both ends as illustrated schematically in FIG. 6D. Once theelectric field has brought the two nano-wires in sufficient proximity,the magnetic attraction between the Ni segments at the ends may securelyjoin the two nano-wires, even after the electric field is turned off.

Nano-wires are promising building blocks for microelectronics. Tointegrate nano-wires as active elements in circuits, a technique mayselect nano-wires to serve as transistors or interconnects. Further, thetechnique may position nano-wires with high precision in controlledalignment. In addition, the technique may dissemble nano-wires on demandto re-configure circuits.

This technique was demonstrated on an array of nano-pillars. Eachnano-pillar, as shown in FIG. 7A, was a sandwiched structure integral toa substrate. For example, a Cr layer (bottom) may be the adhesive layerfor on the substrate using lithographic techniques. The bottom layer mayalso become integral to the substrate by other processes withoutdeviating from the general concepts of the current invention. A Ni layerin the middle may provide a magnetic force, and a gold top layer mayadjust the magnitude of the magnetic force imposed on top of thenano-pillar.

To magnetize the nano-pillars, an external magnetic field was temporallyimposed to and then subsequently removed from the nano-pillars. However,a permanent magnetic segment may also be used. In this example shown inFIG. 7A, Au nano-wires with Ni segments in the middle wereelectrodeposited. Using the precision manipulation technique, the Aunano-wires were transported and mounted on top of all 16 lithographednano-pillars, as shown in FIG. 7B. All of the nano-wires preferentiallyaligned in the direction of the external magnetic field that magnetizedthe nano-pillars. These assemblies of nano-wires mounted on nano-pillarsremained intact even after the evaporation of the fluid medium. Aclose-up view of the assembled nano-structure is shown in FIG. 7C. Thenano-wires were precision positioned such that the Ni segments ofnano-wires were flush with the edges of Ni segments of the nano-pillars. The nano-wires may be surface processed to be electricallypolarizable, as, for example, electrical dipoles or electricalquadruples.

Using this technique, nano-wires can be directly integrated into acircuitry of, for example, sensors, detectors, logic units, etc.Heterogeneous nano-wires can be assembled into the same circuitry, someas transistors and some as interconnects. By manipulating the magneticconfiguration of nano-magnets to turn the magnetic field from thenano-magnet on and off, the nano-wire circuitry can be disassembled andreconfigured

FIG. 8A shows a nano-motor assembled according to an embodiment of thecurrent invention. The magnetic attractions between the magneticsegments in the nano-wires and the nano-pillars serve as the bearingsthat pivot the rotating nano-wires at fixed positions. Thus, orderedarrays of nano-motors can be assembled.

FIG. 8B shows measured rotation angle and angular rotation speed of thenano-motor of FIG. 8A according to some embodiments of the currentinvention. The rotation angular speed has two states, a high speed stateand a low speed state. The duration of each state is 360 degrees inrotation angle. This is because the magnetic torque in the bearingchanges every 360 degrees. In addition, the speeds associated with thehigh speed and low speed state increase with V² linearly, as shown inFIG. 8C.

FIG. 8D shows an array of the nano-motors according to an embodiment ofthe current invention. The positioning of the nano-wires mounted on thenano-pillars c an be precisely controlled by the electric fieldtransport technique. The initial alignment direction of the nano-wirescan be controlled by tuning the magnetic orientation in the magneticbearing.

FIG. 8E shows a 2 x 2 array of the nano-motors in an induced rotarymotion according to an embodiment of the current invention. Overlappedimages of the array from a camera (at a frame rate of 0.1 second)demonstrate that 75% of the assembled nano-motors were in successfulrotation, indicating a great yielding rate. By precisely tuning thelength of the magnetic section in the nano-wires, the diameter and thelayer thickness of the magnetic bearings, an improved yield rate of over90% may be expected. Moreover, a lubricant layer on at least one of thenano-wire and the nano-pillar can decrease friction between the twonano-structures during operation of the nano-motor. The nano-motorsaccording to some embodiments of the current invention can be used invarious applications involving MEMS and/or NEMS devices such asmicrofluidic mixing, microfluidic pumping, fluidic sensing, and choppinglight.

The method of rotating a type of nano-motor has been disclosed in PCTpatent application No. PCT/US2005/033972, the entire contents areincorporated by reference herein.

Using the manipulation method of the current invention, the nano-wirescan be assembled into various NEMS/MEMS devices. FIG. 9A shows anano-wire oscillator assembled according to an embodiment of theinvention. This V-shaped nano-structure was formed by joining twooppositely charged Ni/Au/Ni nano-wires end to end while the other twoends were integral to the quartz substrate by non-covalent bonds betweenNi and quartz. This nano-structure with two anchoring points on thesubstrate can be driven into mechanical oscillations by AC square-wavevoltages (1˜2.5V). The position of the oscillator, as characterized bythe angle between the plane of the oscillator and the normal directionof the substrate surface, can be measured from the projection length ofthe nano-structure. FIG. 9B shows the photos of the nano-structure atvarious angles during the oscillation. FIG. 9C reveals the oscillationwas at frequencies from 0.5 to 2.5 Hz, identical to that of the ACsquare wave frequency. These oscillators operated in water and can hencebe relevant to biomedical applications. These oscillators have beenentirely assembled in situ from individual nano-wires using EP and DEPmanipulation.

Thus, a method of precision transport of nano-structures in suspensionwith sub-micrometer accuracy using a combination of the electrophoretic(EP) force and the dielectrophoretic (DEP) force has been described.Using this method, nano-structures can be efficiently incorporated intodevices as active elements for sensors, detectors, and logic units, forexample. Nano-wires are also important building blocks formicro/nanoelectromechanical system devices (MEMS/NEMS). Nano-motor andnano-wire oscillators have been assembled by using this precisiontransport technique. Attaching additional nano-structures to theassembled nano-structures described above may enable more MEMS/NEMSdevices. For example, by adding a nano-shaft to the nano-wiremicromotor, a MEMS/NEMS device may be assembled that translates arotational motion into a linear oscillation. It is anticipated that avast range of multi-component nano-structures can be produced by thesemethods, many of which have analogies with macroscopic mechanicaldevices. The broad concepts of the current invention are not limited tothe particular examples provided.

In describing embodiments of the invention, specific terminology isemployed for the sake of clarity. However, the invention is not intendedto be limited to the specific terminology so selected. Theabove-described embodiments of the invention may be modified or varied,without departing from the invention, as appreciated by those skilled inthe art in light of the above teachings. It is therefore to beunderstood that, within the scope of the claims and their equivalents,the invention may be practiced otherwise than as specifically described.

1. A method for assembling multi-component nano-structures, comprising:dispersing a plurality of nano-structures in a fluid medium; applying anelectric field having an alternating current (AC) component and a directcurrent (DC) component to the fluid medium containing the plurality ofnano-structures, wherein said electric field causes a firstnano-structure from said plurality of nano-structures to move to apredetermined position and orientation relative to a secondnano-structure of said plurality of nano-structures such that said firstand second nano-structures assemble into a multi-componentnano-structure.
 2. The method of claim 1, wherein said fluid mediumconsists essentially of de-ionized water.
 3. The method of claim 1,wherein each nano-structure of said plurality of nano-structures has alongitudinal dimension of less than 100 μm and a lateral dimensiongreater than 2 nm and less than 400 nm.
 4. The method of claim 1,wherein each nano-structure of said plurality of nano-structures has alongitudinal dimension of less than 10 μm and a lateral dimension ofgreater than 5 nm and less than 100 nm.
 5. The method of claim 1,further comprising: monitoring positions and orientations of said firstand second nano-structures during said applying said electric field; andchanging said electric field based on said monitoring.
 6. The method ofclaim 1, wherein said second nano-structure is integrally connected to asubstrate.
 7. The method of claim 6, wherein said first and secondnano-structures each have a section of a magnetic material.
 8. Themethod of claim 7, wherein said first nano-structure and secondnano-structure assemble into said multi-component nano-structure througha magnetic interaction of said sections of magnetic material.
 9. Themethod of claim 6, further comprising applying a magnetic field toselectively orient magnetic poles of said first nano-structure relativeto magnetic poles of said second nano-structure.
 10. The method of claim1, further comprising surface processing said first nano-structure tocause said first nano-structure to be at least one of electricallycharged, electrically polarized or electrically polarizable.
 11. Themethod of claim 10, wherein said surface processing comprisesconjugating at least one of a thiol group, a carboxyl group, an aminogroup, or equivalents thereof.
 12. A system for assemblingmulti-component nano-structures, comprising: a sample holder defining asample chamber therein, said sample chamber being suitable to hold afluid having a plurality of nano-structures suspended therein; first andsecond electrodes spaced apart with said sample chamber arrangedtherebetween; a voltage source electrically connected to said first andsecond electrodes; and a voltage controller in communication with saidvoltage source, wherein said voltage source is suitable to provide a DCvoltage and an AC voltage in response to said voltage controller tocause a nano-structure of said plurality of nano-structures to becomeoriented in a predetermined orientation and to move to a predeterminedposition.
 13. The system of claim 12, further comprising third andfourth electrodes spaced apart with said sample chamber arrangedtherebetween and electrically connected to said voltage source, whereinsaid first, second, third, and fourth electrodes are arranged to provideselected AC and DC voltages within a plane for at least two-dimensionalorientation and positioning of said nano-structure.
 14. The system ofclaim 12, further comprising fifth and sixth electrodes spaced apartwith said sample chamber arranged therebetween and electricallyconnected to said voltage source, wherein said first, second, third,fourth, fifth, and sixth electrodes are arranged to provide selected ACand DC voltages within a volume for three-dimensional orientation andpositioning of said nano-structure.
 15. The system of claim 12, furthercomprising an observation system arranged to monitor positions of saidplurality of nano-structures in said sample chamber.
 16. The system ofclaim 15, wherein said observation system is an optical observationsystem and at least one of said first and second electrodes issubstantially transparent in an operating wavelength range of saidobservation system.
 17. The system of claim 15, wherein said observationsystem is further adapted to recognize changed positions of said nano-structures and to provide said controller with a signal indicative ofthe changed positions.
 18. The system of claim 15, wherein saidobservation system comprises at least one of a microscope, a CCD camera,an infra-red camera, and a radiation detector.
 19. The system of claim12, wherein said plurality of nano-structures comprise at least one of anano-wire, a nano-fiber, a nano-tube, a nano-sphere, a nano-disk, anano-plate, a nano-cube, a nano-cylinder, a nano-pillar and variantsthereof.
 20. The system of claim 12, wherein said sample chamber is lessthan 1 mm in length.
 21. The system of claim 12, wherein said voltagecontroller comprises a computer having a processor, a memory, a displaydevice, and an input device.
 22. A multi-component nano-structure,comprising: a first nano-structure having a first magnetic segment; anda second nano-structure having a second magnetic segment, wherein saidfirst and second nano-structures form a multi-component nano-structurevia an interaction of said first and second magnetic segments.
 23. Themulti-component nano-structure of claim 22, wherein said first andsecond nano- structures each have a longitudinal dimension that is lessthan 100 μm and a lateral dimension of at least 5 nm and less than 400nm.
 24. The multi-component nano-structure of claim 22, wherein saidfirst and second nano- structures each have a longitudinal dimension ofless than 10 μm and a lateral dimension of at least 5 nm and less than100 nm.
 25. The multi-component nano-structure of claim 22, wherein atleast one of said first and second nano-structures have a layer of anon-magnetic material that provides a spacer to contribute to providinga preselected strength of said interaction between said first and secondmagnetic segments.
 26. The multi-component nano-structure of claim 25,wherein said first nano-structure is one of a nano-wire and a nano-tubeand said second nano-structure is a nano-pillar integrally attached to asubstrate, said first nano-structure being rotate-ably attached to saidnano-pillar to form a nano-motor.
 27. The multi-component nano-structureof claim 26, further comprising: a lubricating layer on at least one ofsaid first and second nano-structures to decrease friction between saidfirst and second nano-structures during operation of said nano-motor.28. The multi-component nano-structure of claim 25, wherein said firstand second nano- structures are attached to each other at one end andmoveably attached to a substrate at opposing ends such that saidmulti-component nano-structure provides a nano-oscillator.